Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$207.85	12.156%	$233.1162	$233.12	$233.10	$233.10
Purchase #2	$50.77	6.379%	$54.0086	$54.01	$54.00	$54.00
Purchase #3	$159.39	13.463%	$180.8487	$180.85	$180.85	$180.80
Purchase #4	$32.31	4.635%	$33.8076	$33.81	$33.80	$33.80
Purchase #5	$202.77	12.240%	$227.589	$227.59	$227.60	$227.60
Purchase #6	$77.58	12.366%	$87.1735	$87.17	$87.15	$87.20
Purchase #7	$53.89	10.615%	$59.6104	$59.61	$59.60	$59.60
7 purchase totals =	$784.56		$876.1540	$876.16	$876.10	$876.10